There have been numerous attempts to develop a spinal implant to replace a damaged or degenerated natural spinal disc and to maintain sufficient stability of the intervertebral disc space between adjacent vertebrae, at least until arthrodesis is achieved. These types of spinal implants have taken many forms.
For example, some spinal implants are designed to expand in such a manner as to restore and/or maintain the natural anatomic angle between the adjacent vertebrae. To accomplish this result, some implant designs include multiple branches having stationary ends that are attached or otherwise coupled together and movable ends that remain unattached so as to allow the movable ends to expand apart relative to one another to provide the implant with a select taper angle corresponding to the natural anatomic angle between the adjacent vertebrae. Expansion of the implant typically relies on axial displacement of an expansion member or wedge along tapered inner surfaces defined by the branches. One example of such an implant design is illustrated and described in U.S. Pat. No. 6,436,140 to Liu et al., the contents of which are incorporated herein by reference.
Expandable spinal implants typically rely on relatively slender or weakened structures or features that allow for material deformation of certain portions of the implant, which in turn facilitates expansion of the implant in one or more directions. However, the slender or weakened features that allow for material deformation tend to compromise the structural integrity of the implant and reduce resistance to loading, particularly resistance to buckling and shear loads exerted onto the spinal implant by the adjacent vertebrae. Accordingly, incorporation of features into the spinal implant which facilitate expansion may result in a reduction in the overall structural integrity of the implant.
Thus, there is a general need in the industry to provide an improved expandable spinal implant. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.